An ultrasonic flow meter including a straight tube-shaped tubular body for measurement through which a fluid for measuring a flow rate flows has been conventionally known (for example, see Japanese Unexamined Patent Application, Publication No. 2012-42243 (hereinafter referred to as “JP 2012-42243”)). The ultrasonic flow meter disclosed in JP 2012-42243 has a structure in which a pair of ultrasonic wave oscillators is disposed at a predetermined interval on the outer periphery of the straight tube-shaped tubular body for measurement. The ultrasonic flow meter disclosed in JP 2012-42243 is used exclusively for measuring a flow rate, and does not have a function of adjusting the flow rate of a fluid.
When the function of adjusting the flow rate is added to the ultrasonic flow meter disclosed in JP 2012-42243, the portion of the straight tube-shaped tubular body for measurement corresponds to a portion where ultrasonic waves transmitted from the pair of ultrasonic wave oscillators are propagated. In this portion, the flow rate adjustment cannot be performed. Accordingly, when the function of adjusting the flow rate is added to the ultrasonic flow meter disclosed in JP 2012-42243, it is necessary to connect an additional flow rate adjusting device to the downstream side of the ultrasonic flow meter.